To prevent unauthorized opening of a container and counterfeiting of contents thereof, RFID (Radio Frequency Identification Device) tags are conventionally disposed on a cap covering an opening of the container.
For example, the cap described in Patent Document 1 (identified below) is made of a plastic material and has an RFID tag disposed on the back side of a top plate part thereof.    Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-525930.
If a cap is made of a non-metal material such as a plastic material as is the cap described in Patent Document 1, the RFID tag provided inside the cap can communicate with a communication device outside the cap. However, If the cap is made of a metal material and the RFID tag is disposed inside the metal cap, the RFID tag cannot communicate with a communication device outside the cap.
If an RFID tag is provided outside the metal cap as a countermeasure, the RFID tag can easily be removed, which may make it unable to prevent unauthorized opening of a container and counterfeiting of contents thereof.